Supersonic transducer

ABSTRACT

A supersonic transducer including means for detecting its vibrating speed and for changing the frequency of the energizing current in response thereto. This invention utilizes the property that when an electrostrictive vibrator is vibrated resonantly, its dynamic admittance varies depending upon the difference in its stress distribution. The electrostrictive vibrator is divided into portions of large and small stresses to cancel the applied brake currents. Simultaneously, a signal is derived that is proportional to the difference of the dynamic currents so as to provide an effective energization by detecting the resonant frequency of the vibrator in order to automatically adjust the applied frequency of the supersonic transducer.

Patent 11 Mlsltlro 1-5 1 1 surmsomc n/ nsnucsn [75] Inventor: Sltojl Mlshlro, Tokyo. Japan [731 Assignee! Tap ElectrieCm. Ltdwfl'okyo. Japan t 1221 Filed: Mu. 2a. 1973 1211' Appl. No.: 345,530

32 us. c1 310/31, 310/93. 310/87. 313/11 331/163 1511 1111. c1 H04r 1 1/00 [58 1 16111 or Search 31019.7. 9.8, s. 8.1. 3.1; v 318/116; 331/163. 164

- 56 References Cited UNITED STATES PATENTS 1.912.213 5/1933 Nicolson 331/163 X 2.309.083 1/1943 Usselman .5331/163 X 2.616.223 1l/l952 Junker 310/).8 2.848.672 3/1958 Harris 318/116 X 3.117.768 1/1964 Carlin 310/8.1 X 3.432,?73 3/1969 Land et a1 .3 331/163 X 3,489,930 1/1970 Shoh 310/8 1 FOREIGN PATENTS 0R APPLlCATlONS 842.674 5/1952 Germany 331/163 Primary Examiner-Mark Budd I Attorney. Agent. or Firm-Oblon. Flsher Spilqnk. McClelland & Muier 1 tor in order to automatically adjust the applied -frequency of the supersonic transducer. 1

7 Claims, 17 Drawing Figures ing resonant frequency.

"2. Description of the Prior Art pact electrostrictive element.

. m a'supersonictransducerwhieh a 'simple'com- -.At'urther objec t ofthe sun another object-of this invention ,is to provide supersonic transducer which provides Tartetlective detecting signallofa circular; rectangular or; cylindrical I electrostrictive vibrator whichdrivesan. energizing power supply.

In an electrostrictive vibrator, piezo-electric electroi strictive materials such as lead titanate zircon'ate are utilized. It is possible to produce various shaped vibra-' tors because the powder of the above electrostrictive material is poured into 'a mold when; produced. For e tample, the vibrator .may have shapes suchas cylindri-v shapes may be produced depending upon its desired utility. Also, since a polarization is applied after it is unglazed, the orientation of the polarization may be freely selected. Since it is a strong dielectric",'its electric capacity is large and, as its electric impedance is very small, the energizing voltage to'be-applied between both electrodes may be small. and accordingly it has characteristics very easily controlled. Thus, it may be utilized in many fields. There is known in the art one type of vibrator known as Langevins vibrator for pro ducing a resonant frequency of several kHz by placing an elect rostrictive vibrator between two metal blocks.

One problem associated with such clectrostrictive=vibr'ators is the variation of resonant frequency of thclvibratoraccording to the temperature and'load conditions. The frequency of the energizing voltage may be displaced thereby, and it may become impossibleto vibrate the device. When the .Q factor generally becomes Still another'object'of this invention is to provide supersonic transducer which. detects fan effective detecting signal in Langevin's vibrator.

Briefly, in accordance with the inyention, a super- "sonic transducer is provided whichiii'cludes means for detecting its'vibrating speed andfor. automatically adjusting the frequency of the exciting current in response threto.-'-Ihe-positive electrode plates adjacent cal, circular disc. rectangular Plate. p r Smaticror other vibralillgelemcm ale d :l q h that a main portionsis adjacent the section of the vibrating element having thelargest vibrational stress. The

other portions ofthe positive electrode plates are made equal in total'area'to the 'area'of the main portion such he esentinv ntio wil beco 'e m r*-ful'a -r-nt high-so that the mechanical resonance of its vibrating i e n i m o h L system is operating at its peak. the foregoing tendency "in which: 40 V frequency. in other words, at detecting pick-up clement is provided in the vibrator. and generally it performs effectively, but since its detected voltage is extremely low, its electrical control is difficult. Also, if the area of the feedback electrode is enlarged, ittendsto vibrate effectively so that it cannot obtain the desired results.

In addition to the above system, there exists in the prior art means for electrical detection by utilizing a bridge circuit, or a known method by" mechanical means. but they require an artificialload, and are difficult to control electrically.

SUMMARY OF THE INVENTION it is therefore amain object of the present invention to provide a supersonic transducer which provides a positive detection signal for vibrating it effectively.

Another object of the present invention is toprovidc a supersonic transducer which may automatically fo llow the frequency of the energizing power supply based on a detection signal that corresponds to the variation thereof 'admittances will be unequal. The difference in detected current between the main portion and the other portions will be indicative of this difference in dynamic admittance, and thus will be indicative of the actual vibrating speed of the vibrating element. Detection and feedback means are provided to adjust the applied sigha] in response to the aforcde's'cribed detected signal 'and thus, vibration will occur at optimum excitation conditions.

BRIEF oEscRu noN or THE DRAWINGS These and other objects. fcatu're s and advantages of from a consideration of the following description when taken in conjunction with the accompanying drawings.

FIG. 1 shows perspective and cross-sectional views of a. conventional circular electrostrictive vibrator vibrating in its radial direction showin'giits-operating state;

FIG. 2 shows perspective and cross-sectional views of .a rectangular electrostrictivevibratdr vibrating longitudinally showing its operating state;

FIG. 3 showsperspective and sectional views of n circular electrostrictive vibrator constructed according to the present invention? FIG. 4 shows perspective and; Sectional views of a rectangular electrostrictive vibrator in accordance with the present invention;

FIG; 5 is a sectional view of thevibrator of the present invention utilized in a cleaner;

FIG. 6 is a sectional view of a cylindrical clectrostric tive vibrator according tothe present invention with an .clectric circuit;

FIG? is a sectional view of Laitgevin's vibrator according to the present invention;

FIG. 8 is a sectional view of another embodiment of the vibrator of this invention; and

MG. 9 is a sectional vicwof a vibrator of thc'pr'ts'cnt invention with an amplitude c pandin'g hum ()iiSCIRlVl'lON ()I' THE PREF'IERRID liMliODlMliN'lS Referring now to the drawings. wherein like ruler tllltit numerals npmscm identical or unrtcspott'rlttttt is to provide 3 parts throughout the several and larly to FIG. thereof, thereis illustrated a conventional circular electrostrictive vibrator comprising an electrostrictive' element 1. and electrode thin films 2 and 3 made of. for example. silver. provided by'a deposition or other method on both surfaces of the electrostrictive element 1, which is polarizedin thethickness direction.

When the vibrator is vibrated through the electrode films 2 and 3 by means of an energizing power supply having a vibrational resonant frequency along the-radial direction of the electrostrictive vibrator. it vibrates in the direction as illustrated by the arrows 4. A radial Y the vibrator in its vibrating direction.

sectional view is shown by-FlG. [(b). the distribution of the vibrating speed of the vibrator is shown in FlG.

. [(c). and the distribution of the vibrational stress isillustrated by FIG. 1(d).

tive vibrator comprising an electrostrictive element and electrode thin films 2 and 3 provided on both surfaces of the electrostrictive.element l for operating in FIG. 2 shows a conventional rectangular electrosttic- 4 a FIG. 4(a) showsone embodiment of a rectangular electrost'rictive vibrator accordingito the present invention which includes means for detectingthe vibrating .trode surfaces ts. is and i! of silverthin films divided f into three as'shQwn-The center portion 17 has a larger vibrating stress perpendicular to the vibrating direction of the vibrator. and both ends-l5 and 16 have I a smaller vibrating stress so that the brake admittance of the center portion and composite brake admittances of both ends with respect to the electrode surface 14 becomes the same. FIG. 4(b) shows a sectional viewof Furthena lead wire 18 is providedfromthe electrode surfaces 15 and I6. a lead wire 19 is provided from electrode surfacefll7, and a lead wire is provided from electrodesurface l4.

p When the lead wires 18 and 19 are connected to one vibrating direction as shown by'arrows 5. The longitu- Q dinal section is shown by FIG. 2(b'), the distribution of .the vibrating speed of the vibrator is shown in FIG.

2(c). and thedistribution of vibration stress is illustrated in H6. 2(d).

Referring nowto FIG. 3, one embodiment of the present invention is shown as a circular electrostrictivc vibrator that is provided with means for detecting its vibrating speed. FIG. 3(a) is its perspective view,, and

FIG. 3(h)'is its radial sectional view.

In the embodiment shown in FIG. 3, there is provided I of the electrostrictive vibrator. a lead wire ll is con nected, to electrode surface 9 and a lead wire 12 is attached to electrode surface 7.

In the electrostrictive vibrator thus constructed, the lead wires 10 ii are connected iu one electrode of an energizing power supply, and the-lead wire 12 is connected to the other electrode thereof. When the frequency of the energizing power supply is tuned with the resonant frequency in the radial direction of the electrostrictive vibrator. the exciting current flowing to the electrode surfaces 8 and 9 becomes the composite current of the currents flowing to the respective brake admittance and dynamic admittance. As is clear from the structure of thcvibrator. however, the electric current flowing to the respective brake admittancesheelectrode of an energizing power supply and the lead wire 20 is connected to the other electrode thereof. and

ponent of theelectric current of the current flowing to the respective dynamic admittance flowing to lead-wire 19 is always larger than that of the current flowing to the lead wire 18 being similar {IQ the embodiment shown in FIG. 3.

Therefore; the difference of the electric currents flowing through lead wires 18 and 19 can be detected the respective dynamic admittance is always larger at I theportion of electrode surface-9 having the larger distribution of the vibrating stress.

Therefore. if the difference between the electric currents flowing through the lead wires l0 and ll is detected by a bridge circuit or a differential current transformer. the difference between the electric currents flowing through both dynamic ndmittanccs which represents the electric signal proportional to he vibrating speed. may be effectively detected. I

by a bridge circuit or a differential current transformer so that the detected signal will be an electric signal proportional to the vibrating speed. 5

Although the embodiment shown'in FIG. 4 illustrates a rectangular electrostrictive vibrator. other shapes of electrostrictivc vibrators may also'embody the principles of this invention as will be clear to. those skilled in the art. I j j Though the respective electrode surfaces divided into two blocks responsive to the vibrating stress are constnicted so as to b equal in their brake admittances in the above embodiments. even if; they-are so constructed that the brake admittances therebctween are different. it will be clearly understood by those skilled in the art that if they are so constructed that the electric current flowing into both brake admittances by a bridge circuit or differential current transformer may be cancelled by each other. that the vibrating speed may be effectively detected in the electrostrictive vibrator in accordance with the teaching herein.

. Referring now to FIG. 5, another embodiment of the circular clcctrostrictive vibraton of this invention is shown in combination with smart: cleaner as a trans dttccr. 3 i

In FIG. 5. a circular elcctrostrictiv'e vibrator having electrode surfaces 22, 23 and 24 orrhoth surfaces of an clectrostrictivc element 21 is mounted through an ad hesivc 26 onto the bottom surface of a cleaner 25. One output terminal 28 of a feedback oscillator 27 is con nected to intermediate tap M of u primary, winding 30 of a differential current transformer 19. Both ends oi the primary winding 30 arc connected to the divnhsd' electrode surfaces 23 and 24. and the other ootput to! minnl 32 of feedback oscillator 27 istooiicrtnd in thc asecondary ing, the exciting current fed from output tenninal 28 of i 1 the feedback oscillator 27 flows through intermediate tap 31 of primary winding of differential. current transformer 29 to the electrode surfaces 23 and 24. The difference of the. exciting current flow through both electrode surfaces 23 and 24 produces a voltage proportional to the vibrating speed in the secondary liquid filled in the cleaning containerZS, the ternperature, or any other external conditions so as to operate the vibrator in an optimum state.

tecting the vibrating speed signal of this invention by cancelling part of the brake admittance of the electrostrictive vibrator against part of the brake admittance of the same electrostrictive vibrator. it differs from the conventional art which typically comprises detection by an external element or separation of the artificial load. The present invention decreases the error based on the temperature difference error due to drive level or change due to aging of the brake admittance. and provides a simple structure along with its remarkable advantages.

FIG. 6 shows still another embodiment of a vibrator in cylindrical shape according to the principles of the present invention. This embodiment of the eleet'rostrictive vibrator has a vibrator body 36 made of piezoelectric electrostrictive material, such as lead titanate zirconate, in cylindrical shape To one endof body 36 is fixed a metal resilient member comprised of a smaller diameter parallel portion 37, an exponentially.

25 The foregoing description illustrates a method of de- 6 f transfon'ner 47 are connected to the; input terminals 58 and 59. respcctively, of the, feedback oscillator 50.

' In the operation of such a' vibrator, if the feedback oscillator 50 is driven by a frequency approximately corresponding to the resonant frequency of the vibrator body 36, the vibrator body 36 resonantly vibrates.

An exciting-voltage isapplied from output terminal SI of feedback oscillator 50 through primary winding 48 of differential current transformer to center electrode 44 and end electrodes 45. and 46, thus energizing the vibrator. Since the total area of the center electrode 44 and end electrodes '45 and is substantially the same as that of thecommon electrode 42, very effective energization is achieved. Since the electric current flowingithrough the center electrode 44 and the end electrodes 45'and 46 are in series opposition in the primary windirig'.48, the-electric fcurren't based on the brake admittance of the center electrode 44 and that based on the brake admittancesof the end electrodes 45 and 46 will be the same in value, and accordingly there will not be produced any induced current in the secondary winding-55 of the transformer. The brake admittance may simply increase in response to the frequeney, but since the frequency conditions of both are the same in this case. itn'eed not be considered. Distortions produced at the center of center electrode 44 and at the ends of end electrodes 45 and 46 are different during the energization of vibrator body 36 such that the internal stress is larger at the center than at the ends. As a result, the dynamic admittance atcenter electrode 44 is far larger than those of electrodes 45 and 46 so that the electric current flowing'from intermediate tap 49 to terminal '53. of differential current transformer 47 is larger than that flowing from intermediate tap 49 to terminal 54. Accordingly. the electric current based onjthc dynamic admittance will be the difference between the current'iri center electrode 44 and end terminals 45 and 46,50 that the induced current based on this difference flows through the secondary winding 55. Since the electric current flowing through the secondary winding 55 has the characteristie that it changes frequency according to the dynamic v admittance. its valu'ecorrcsponds to the state of resoshaped portion 38am! a larger diameter parallel porequal to the combined areas of the endelectrodes 45 and 46, and the brake admittance of the common electrode 42 is determined so as to equalize the same.

This vibrator is also provided with a differential current transformer 47 as detecting means. An output'terminal 5! of the feedback oscillator 50 being'an energizing' power supply is connected to the intermediate tap 49 disposed along the primary winding 48 of the differ ential current transformer 47. The other output terminal $2 is grounded. The terminal 53 of primary winding 48 is connected to center electrode Miami the other terminal 54 is connected to end electrodes 45am] 4b.

nant vibration of vibratorbody Therefore itis seen that the vibratings'pe'ed can bedetected by measuring the current valuefif r Sincelterminals 56 and 57 of secondary winding are connected to input-terminals S8 and 59 of feedback oscillator 50, the signal based onthe vibrating speed of the vibrator body 36- isfalwaysfed back. Feedback oscillator 50 is controlled thereby so as to produce an output of the oscillating frequency that follows the vi brating speed of the vibrator body 36. Thus. the detect ing signal is given to feedback oscillator!" in order to provide automatic frequency control.

The brakeadmittances of center electrode 44 and end electrodes 45 and 46 of vibrator body 36 may not always coincide with cach othcr so as to produce the above desired results. Howevcnt hc device may be con structcd so {[5 to cancel the-electric current by an electrical treatment at the detectingpdi tion. As to the dc testing portion. a bridge circuit may be utilized instcad of the differential Current transformer. iintli in fact not 1 The common electrtidedliii groundedas shtiivnfl'hc terminals 56 and 57 ofthc secondary winding 55 of means which picks up the sigmilpmtmrtionul to the vhf nnniii: admittance may; he \lllllltltl.

it should he understood from the for-upon! descrip tion that hillt't inc vibrator of this invention has the 7 M l center and end electrodes on one peripheral surface of the cylindrical vibrator body used as the energizing electrodes and is simultaneouslyconnected to the detecting portion for picking up the signal proportional to ,the electric current based on the dynamic admittance while cancelling the brake admittance, it may effectively obtain the detecting signal while effectively driving it. Thus, it is not necessary to provide the pickup element only for detecting an artificial load as seen in the prior art detecting devices so that the present structure is seen to be more simple in its operation. Also, a detecting signal having. a sufficient output is readily 'obtainable and further the present invention sufficiently eliminates errors in the detecting of thevibrating speed such as an error based on the temperature difference from the artificial load, error of the driveflevel, or error On'the' other hand, electric currents tlowinginto the brake-admittance of electrostrictive elements 60 and which have the same characteristics. are the same. 4 I

Therefore, if an electricisignal proportional to the difference between the exciting currents flowing into electrostrictive elements wander are fed to a bridge circuit or a differential current transformer, an electric signal proportional to the difference of the electric current flowing into the dynamic admittances ofclectrostrictive elements wand 61, that is, the electric signal =proportional-;to the vibrating speed of the Lange'vin's vibratorl may be effectively detected.

The resilient insulator 64 in the aboveembodiment is preferably made of resilient material having favorable heat conductivity and electric insulation characteristics such as, forexample, athintilm printed substrate of alumina porcelaimberyllia porcelain, or epoxy resin containing copper foil'glass fiber on both surfaces thereof as an insulator adjacentelectrode plates 62 and M I 63 so as to facilitate easy heat exchange between the electrostrictive elements 60 and 61. The voltage applied to' both surfaces of any resilient insulator is small,

titanate zirconate. electrode plates 62 and 63, and a resilient insulator 64 interposed between the annular electrostrictive elements 60 and and the "electrode plates 62 and 63, as shown. A circular cylindrical metal. resilient body 66 having a bolt 65 at thecenter axis 1 thereof is also provided in combination with a circular cylindrical metal resilient body 67 having a center hole tightened from both sides of the electrostrictive elements 60 and 61 by bolt 65, washer 68 and nut 69. The axial length of the circular cylindrical resilient body-66 excluding the bolt 65 is-s'e lected to be substantially onefourth of the wavelength of the intrinsic resonant freclude the provision of the resilient insulator 64 added with the electrode plates 62 and 63 facing oppositely to the eiectrostrictive elements 60 and 61. Further, an-

. other important feature is that the electrostrictive elements 60 and 6t arearranged at positions which are different in stress distribution along the axial direction of the vibrator.

In this embodiment, if electrostrictive elements 60 and 6! are connected in parallel, that is, the electrode plates 62 and 63 are connected to one electrode of-the energizing power supply and the circular cylindrical metal resilient bodies 66 and 67 which are in contact thus its voltage endurance is not a problem and there fore, sufficiently thin material may be utilized.

ltis, of course, possible that resilient insulator 64 can be omitted. Then, bolt 65 and circular cylindrical metal contacting with both outer surfacesof the electrostrictive elements 60-and 61 constituting another electrode, so as to operate it within the spirit and scope of the present invention. L

FIG. 8 shows another enibodimentof the electrostrictive vibrator comprised of four electrostrictivc elements which does not require the resilient insulator 64 as seen in the embodiment shown in FIG, 7.

Referring now, to H6. 8.-annular electrostrictive elements 60,61, and 7| of the samecharacteristics are superimposed by changing the' polarizing direction stcp by step through electrode plates 72, 73 and 74, respectively, and are tightened from both outside surfaces thereof by the metal resilient bodies 66 and 67 by means of bolt 65, washer 68 and nut 69. Electrode plate 73-is connected through the metal resilient body other electrodes of the cnergiiingpowcr supply.

with the other surfaces of elements) and 6t. respcc- -tr0de current flowing into the elcctmstr'ictivc clement 6l"disposerl at the part having the smaller vibrating stress i The difference of the current flowing from electrode plate 72 to the electr'ostrictive elements 60 and M and that flowing rom electrode plate 74 to clcctrostn'ctiw elements 70 and 71 may be detected as the signal pro- .cssarily limit their positions they may be disposed more in the vicinityof the end surface FKL 9 shows still another embodiment of the ulna tor in combination with a stop horn having a woven I tional exponential step portion. in which-part l th brator is formed to a required shape, as w ll become up patent hereinafter.

, In no. sail metalresilient an CdlitPt'ilQd are inn and to ms-d by a I diameter parallel, 75. an exponential step 16 Letters Patent the United Sta'tes: r

L A iconic transueerthatvibrate'sin to ani a ip'plied electric signal comprising: I a electrostrictive'element having ajpair of vibrating u fa es 7 acanam elecuude surface positioned adjacent one surface of said electrosftrictiveelement.

' a positive electrode surface comprisinga first a second portion positioned adjacent the surface of fisaidelectrostrictive element opposite to said-one surface, j I I I I v I ,means' for applying the common; component of-the' signal to said common electrode surface and the positive .component of the signal to, the first and second portions of said positiveelectrode surface,

' and a large diametenpa'rallel 77, and a metal I resilient body'ltthaving the same, diameter as that of the" larger diameter parallel portionJT tightened in 5 1 asandwieh fashion aroundtheelectrostrictive elements I I (round 61, resilient insulator flandelectrode plates 62 *and 63 by means of a bolt 7, a. iiiatthe vibrating speed of the smaller diameter end surface is increased. from the vibrating speed [of the larger diameter end surface. f i I In FIG. 9, means forfdetecting the vibratingspeedrby I I a differential current transformer 80 is illustrated; An

' intermediate tap 82 is provided to'a primary winding 81 and is connected to the one electrode of the energizing power supply 83. and bothends of the primary winding 8i are connected to the electrode plates 62 and 63 of the vibrator. The other electrode of the energizipg power supply 83 is connected to the metal resilient body 78.

The differential current transformer 80 is so constructed that the voltage drop produced at the primary winding M is sufficiently small compared with the ex citing voltage of the energizing power supply 83.

A load 85 is connected to both ends of the secondary winding 84 of the differential current transformer 80 so that a detection signal proportional to the vibrating speed is obtained. l

The positions of the electrostrictive elements 60 and 6| are displaced from the node portion of the amplitude of the vibration toward the large diameter end 'surface. and since the difference of the stresses applied to the respective electrostrictive elements becomes large. the detection signal indicative of the vibrating speed also becomes large.

In the above embodiment. although the electrostrictive clement group divided totwo sets of blocks responsivc to the vibratingstress is constructed sons to be equal in brake admittance of the respective blocks. even if the brake admittanccs'of the respective blocks are constructed so as to be different. if it is nevertheless constructed so that the currentflowing into both brake admittanccs may be cancelled by a bridge circuit or dif- I ferential current transformer, the Langevins electroa l f 'l cuncmirzfnsfomler r feeding h strictive vibrator may still effectively dete'ctthe vibrat- 45 W compmem 9 Smd appl'ed slgnai to Sam mg spcdd I I tive electrode stirface and detecting an output Si According to the present invention, the vibrator adrePresemIatlvc 0f 'l f m bored by the adhesive in the conventional Langevin's y m adImnmnce of the first p f andm? y' vibrator may elfectively detect the vibrating speed rem? admlllimce of l PQ Q I gardlcss of the construction of the bolting of the outer 59 a fei-dback'oscllmm for receiving said ouipul 5 pcriphcry semen from said differential currenttransformer and for The errors of the detection of he vibrating speed adjusting the frequency of m applisd'ciecttic g, I

' produced by the detecting element. the artifical load. mil in respmse were Q the temperature difference of the vibrator. the differ A supefsonic "ansducei in Cwfdaficfl will claim ence in temperature characteristics. or lack of coinci- 'Whfimifl Said il'imtifmmcl' colllpfifiesi the first portion of said positive-electrode surface being positioned adjacent the section of said ele-. ment which has a vibrating stress which is larger than an adjacent vibrating stress in said element, the second portion of said positive electrode surface being positioned adjacent the section of said ele' I ment which'has a vibrating stress which is smaller than an'adjacentvibrating stressin said element. the surface area of said first'portion being equal to the surface area of said second portion so that the brake admittancefof said first portion is equal to- I the, brake admittance of said second portion, I means for detecting the difference between the dynamic admittance of the first portion and the dy namic admittance of the secondportion. means for adjusting the frequencyof the applied electric signal in response to the dynamic admittance of the first portion and thedynamic admittanceof the second portion. 2. A supersonic transducer in acco'rdahcewith claim I. wherein the second portion of said positive electrode 40 surface comprises two separate sections. I

3. A supersonic transducer in accordance with claim l. whereinsaid frequency adjusting means comprises:

vcntion. Also. the elcctroatrictive vibrator of the pres- 6 I 10 Mid ficflulld P a ent invention may be simply constructed and is of low an intermediate tap for receiving the positive compoinst: I 1 v nent of said applied electric signal of said feedback.

Obviously". numerous modifications and variations of oscillator andtecding il'to said primary winding. the present invention are possible in light of the above a secondary winding positioned to detect a voltage teachings it is therefore to he understood that within m proportional to the difference i'ncurrent in said two dance of various conditions such as the drive level. etc, apparent in the detecting device of conventional elec-v trostrictive elements. are eliminated by the present in-- the scope of the appended claims the invention may be practiced otherwise than as specifically described herein 7 a primary winding having two output wires, one of which is connected to said first portion of said positive electrode surface. the other of which is con output wires of said primary winding. said secondary winding having two output wires connectedto the input term nals of said feedback oscillator 

1. A supersonic transucer that vibrates in response to an applied electric signal comprising: an electrostrictive element having a pair of vibrating surfaces, a common electrode surface positioned adjacent one surface of said electrostrictive element, a positive electrode surface comprising a first and a second portion positioned adjacent the surface of said electrostrictive element opposite to said one surface, means for applying the common component of the signal to said common electrode surface and the positive component of the signal to the first and second portions of said positive electrode surface, the first portion of said positive electrode surface being positioned adjacent the section of said element which has a vibrating stress which is larger than an adjacent vibrating stress in said element, the second portion of said positive electrode surface being positioned adjacent the section of said element which has a vibrating stress which is smaller than an adjacent vibrating stress in said element, the surface area of said first portion being equal to the surface area of said second portion so that the brake admittance of said first portion is equal to the brake admittance of said second portion, means for detecting the difference between the dynamic admittance of the first portion and the dynamic admittance of the second portion, means for adjusting the frequency of the applied electric signal in response to the dynamic admittance of the first portion and the dynamic admittance of the second portion.
 2. A supersonic transducer in accordance with claim 1, wherein the second portion of said positive electrode surface comprises two separate sections.
 3. A supersonic transducer in accordance with claim 1, wherein said frequency adjusting means comprises: a differential current transformer for feeding the positive component of said applied signal to said positive electrode surface and detecting an output signal representative of the difference between the dynamic admittance of the first portion and the dynamic admittance of the second portion, a feedback oscillator for receiving said output signal from said differential current transformer and for adjusting the frequency of the applied electric signal in response thereto.
 4. A supersonic transducer in accordance with claim 3, wherein said transformer comprises: a primary winding having two output wires, one of which is connected to said first portion of said positive electrode surface, the other of which is connected to said second portion, an intermediate tap for receiving the positive component of said applied electric signal of said feedback oscillator and feeding it to said primary winding, a secondary winding positioned to detect a voltage proportional to the difference in current in said two output wires of said primary winding, said secondary winding having two output wires connected to the input terminals of said feedback oscillator.
 5. A supersonic transducer in accordance with claim 1, wherein said electrostrictive element comprises a circular disk, said common electrode surface is positioned on one major surface of said electrostrictive element, said positive electrode surface is divided into a centrally positioned circular portion and a ring-like portion surrounding said circular portion, said circular portion and said ring-like portion are positioned on the opposite major surface of said electrostrictive element.
 6. A supersonic transducer in accordance with claim 1, wherein said electrostrictive element comprises a rectangular parallelepiped, said common electrode surface is positioned on one major surface of said electRostrictive element, said positive electrode surface is divided into one centrally positioned rectangular portion and two rectangular portions which are positioned adjacent said centrally positioned portion, the centrally positioned portion and the two rectangular portions are positioned on the opposite major surface of said electrostrictive element.
 7. A supersonic transducer in accordance with claim 1, wherein said electrostrictive element comprises a hollow cylindrical tube, said common electrode surface is positioned on one major cylindrical surface, said positive electrode surface is positioned on the other major cylindrical surface and is divided into one centrally positioned cylindrical portion and at least two adjacent cylindrical portions. 